1. Field of the Invention
The present invention relates to a technique for reading a signal from an image sensor in an imaging apparatus.
2. Description of the Related Art
In recent years, the digitization of imaging apparatuses, such as digital cameras or digital video cameras, has become common and a method of recording an image of an object, as an image signal, on a recording medium using a highly integrated camera has been actively used. In the cameras (imaging apparatuses), automatic focusing (AF) and electronic zooming are electronically set and performed.
For AF, there is a method of reading an object as an image signal, measuring a position of a lens where the object is in focus while changing the lens position, to set the lens in an optimum position, and, when a shutter button is pressed, performing photographing in that lens position. In this type of AF method, since it is highly possible that an object is present in the center of a screen, signals from a region in the vicinity of the center of the screen are taken out to detect a focusing state, and, based on a result of the detection, an optimum position of the lens is obtained to perform photographing.
For electronic zooming, signals from a region at the center of an image sensor and on the periphery of the central are obtained to perform zooming to a screen size using a zoom controller, so that a zoomed image can be obtained.
Meanwhile, in imaging apparatuses, in order to increase resolution, a reduction in the cell size of an image sensor using a fine processing technology is being vigorously performed. Attention is being given to an amplification-type imaging apparatus configured to amplify a signal and output the amplified signal so as to solve a problem of a decrease in output signal level due to a reduction in cell size of the image sensor. Such an amplification-type imaging apparatus includes, for example, an imaging apparatus having mounted thereon an XY address-type sensor, such as a base-stored image sensor (BASIS), a metal-oxide semiconductor (MOS) sensor, a silicon intensified target vidicon (SIT), an amplified MOS imager (AMI), or a charge modulation device (CMD). These image sensors have a feature of being able to capture an image signal from an arbitrary region of the image sensor. For example, Japanese Patent Application Laid-Open No. 2000-209509 discusses an imaging apparatus capable of outputting signals from an arbitrary region of an image sensor during AF to implement high-speed AF.
In an image sensor, such as the one described above, that is capable of performing fast reading of a necessary screen region by capturing signals from an arbitrary region of the image sensor, a signal reading start position or a signal reading end position can be defined to enable capturing of an image from an arbitrary region of the image sensor. However, if the number of defined signal reading start positions or signal reading end positions increases, the size of an imaging apparatus increases accordingly which works against fulfilling miniaturization of the imaging apparatus.